Satan’s power is not unlimited. (CCC 395). The evil spirit cannot directly influence human will and intellect, nor does he know the secrets of the human conscience. He cannot interrupt the construction of the Kingdom of God. His actions are limited by God’s Providence and man’s good will.
Devils’ characteristic features
It must be remembered, however, that devils have retained their angelic nature with all its attributes. Their abilities far surpass those of people, they have a much more developed intelligence, and therefore are able to foresee the future with great accuracy, including the state of human health and the development of events. They possess knowledge of the laws of nature and the physical properties of the created world. They can influence human senses by stimulating natural desires, causing unease, as well as through delusions and nightmares. In some specific conditions they might even cause hallucinations and false revelations, assume the shape of animals, people, angels, or even Jesus and Mary. Satan appeared to St. Padre Pio as nude women, and to St. Faustina as a frightening cat. Stories of simulated apparitions are known, when the evil spirit assumed the appearance of saints and deceived people with a hidden antievangelical message, taking advantage of the visited persons’ vanity and using false spiritual gifts and miracles. Satan, hiding under the guise of good and spiritual development , can lure the gullible into a trap of false mysticism.
Ability to possess
In some circumstances the devil can possess a human, i.e. to take control over their body and use it against the possessed person’s will. A demonic possession is the most visible demonstration of the satan’s power. It is usually the effect of a voluntary choice of evil, persisting in sin or participating in dangerous practices with explicit or implicit occult character. Jesus exorcised the possessed and charged his apostles with conducting this sacramental. Exorcisms must be accompanied by the possessed person’s conversion because, as the Gospel tells us, a devil once cast out can return and do harm with double force if the person does not clear their soul (Matthew 12:43-45). But, when facing sanctity, the true, cowardly nature of the devil is always revealed.